1. Field of the Invention
This invention concerns the stabilization of 3-isothiazolone compounds by the incorporation with those compounds of certain carbonyl compounds.
2. Description of the Prior Art
Isothiazolones have generated high commercial interest as microbicides to prevent spoilage of certain aqueous and non-aqueous products caused by microorganisms. Isothiazolones are highly effective microbicides (as used herein, "microbicides" includes bactericides, fungicides and algicides and microbicidal activity is intended to include both the elimination of and the inhibition or prevention of growth of microbial organisms such as bacteria, fungi and algae); by suitable choice of functional groups, they are useful in a broad range of applications. However, it has been long recognized that either in storage prior to addition to the substrate to be treated or after addition, their efficacy may be decreased because they are not stable under practical conditions of long-term storage. Means have thus been sought for some time to improve the stability of isothiazolones.
U.S. Pat. Nos. 3,870,795 and 4,067,878 teach the stabilization of isothiazolones against chemical decomposition by addition of a metal nitrite or metal nitrate, but teach that other common metal salts, including carbonates, sulfates, chlorates, perchlorates, and chlorides are ineffective in stabilizing solutions of isothiazolones, such solutions usually being in water or in an hydroxylic solvent.
U.S. Pat. Nos. 4,150,026 and 4,241,214 teach that metal salt complexes of isothiazolones are useful because they have enhanced thermal stability, while retaining biological activity.
It is known to use certain organic stabilizers for isothiazolones, generally for use situations where metal salts may create problems, such as corrosion, coagulation of latices, insolubility in non-aqueous media, interaction with the substrate to be stabilized, and the like. Formaldehyde or formaldehyde-releasing chemicals are known as stabilizers, (see U.S. Pat. Nos. 4,165,318 and 4,129,448), as are certain organic chemicals such as orthoesters (U.S. application Ser. No. 118,366) and epoxides (U.S. application Ser. No. 194,234).
Grove, U.S. Pat. No. 4,783,221 teaches blends of isothiazolones with at least one metal salt of an organic carboxylic acid having at least six carbon atoms, wherein the metal is a transition metal, zinc, mercury, antimony, or lead; and also with a solvent diluent.
In certain applications, however, it is desirable to avoid addition of organic stabilizers by virtue of their volatility, decomposition under high heat, higher cost, difficulty in handling, potential toxicity, and the like. Formaldehyde is a suspected carcinogen, and it is desirable not to use formaldehyde in applications where contact with human skin or lungs may occur.
In actual use, copper salts, such as copper sulfate, have proved efficacious in the stabilization of isothiazolones. However, copper salts may be undesirable in effluent streams in such operations as in the manufacture of stabilized isothiazolones or in their blending into a product or the use of that product. Copper salts, especially the chlorides, may contribute to possible corrosion, or in the presence of polymers in aqueous dispersion may lead to coagulation of the dispersion.
German patent application No. 3144137A discloses the use of isothiazolone derivatives to provide bacteriostatic activity in disinfectant compositions containing aldehydes. The minimum ratio of aldehyde to isothiazolone disclosed is 10:1, and there is nothing in the disclosure relating to the stability or otherwise of the isothiazolone.
U.S. Pat. No. 4,539,071 discloses a combination of an isothiazolone and glutaraldehyde as a biocide, but there is no discussion in this disclosure relating to the stability of the composition. Commercial formulations of isothiazolones and N,N-methylolchloroacetamide are also known, being sold under the trademark Parmetol, but the carbonyl compound is not being employed as a stabilizer.